Creates a tag and adds it to the tag table for this.
Equivalent to calling [ctor@Gtk.TextTag.new] and then adding the tag to the buffer’s tag table. The returned tag is owned by the buffer’s tag table, so the ref count will be equal to one.
tag_name is null, the tag is anonymous.
tag_name is non-null, a tag called
tag_name must not already exist in the tag
table for this buffer.
first_property_name argument and subsequent arguments are a list of properties to set on the tag, as with
name of the new tag
null-terminated list of property names and values
name of first property to set
a new tag